I moved out one year ago due to continued disagreements, we bought the house with shared down payments. He lives with his son in the house. Can I wait till he decides to sell and them demand my down payment to be returned or will I loss my down payment. He is on mortgage and I am on deed.

You can do what ever the two of you decide and agree to.

He can not sell the house, unless you sign, so you can demand that

If you are on the deed, you have equal rights with him, regardless of him continuing to pay the mortgage. You need each other's signature to sell.
To avoid expensive legal battles, however, try to get him to sit down with you NOW to work out a plan, based strictly on who has paid what so far.
- down payments are worth what they are
- time lived there is worth 'rent' to yourselves/each other
- mortgage payments paid (not who is on the mortgage) are worth what they are

See if he can afford to buy you out.

I moved out of house that was bought with boyfriend we both put 20,000 down Will I be able to get my down payment back.

How did he get a mortgage without you if both your names are on the deed? Are you sure you are on the deed? But assuming you are. He can't sell the house without your agreement. When the house is sold you get half the proceeds. If you want your money back sooner, he needs to buy you out. And you may have to sue to force him to.